Method of making self-luminous element



` Jan 21,1936- f .n. E. PAUL y -2,028,241

iETEoD' oF MAKING lSELF LUMINoUs ELEMENT" Filed June 15, 1954 INVENTOR ATTORNEYS Patented Jan. 21, 1936 METHOD F OFFICE .mm E. raunNewark, N. J., assigner a United States Radi um Corporation, New York, N. Y.,

a-corporation oi Delaware Application June 15, 1934, Serial No. 'www5 4 claims. (ci. 24o-2.25)

This invention relates to 'self-luminous elements and has particular reference to elements which contain radium compounds so as to be visible in the dark.

It has been the practice heretofore to illuminate indices, pointers, hands, dials, scales, and

other parts of instruments, cr the like, with radium paint composed of small particles of radioactive material dispersed in a suitable adhesive which readily adheres to the surfaces to which it is applied. 'Ihe adhesives used, such as lacquer derivatives mixed with oil, and the like, eventually became discolored, either as theresult of frequent exposure to sunlight, or the deteriorating action of the radium compounds dispersed therein, or to external causes such as gas fumes and the like. 'Ihe luminouspaint accordingly gradually becomes dull with a commensurate reduction of its luminosity of from 50 to 70%, depending upon circumstances. IFurthermore, it is frequently impossible to secure uniformity of application oi' the luminous paint, so that index lines and the like have diierent widths and densities,

with consequent non-uniformity of illumination.

Attempts have been made to overcome the aforementioned objections to luminous paint' by enclosing the luminous material in glass tubes and mounting these tubes on the parts to be illuminated, but because the luminous material loosens and shifts after a time, the luminosity of such tubes becomes non-uniform and their utility accordingly impaired. Impregnating the material in the tubewith an adhesive, as is disclosed in Patent No. 1,364,368, corrects this objection but introduces a deteriorant in the form of the adhesive, so that that expedient does not solve the problem. Also, the presence of air in the tubes when their open ends are sealed by fusion results in the formation of an enlarged ball at that end of the tube, which is objectionable.

In accordance with the present invention, a, self-luminous element in the form of a hermetically sealed capillary tube or capsule containing solidly compacted luminousmaterial in the substantial absence of air is provided, this tube being either circular or flat in cross section, depending upon requirements. The iiat tube is especially advantageous for forming index markers and the like, because it is more readily applied than circular section tubes and gives a 4maximum luminosity for a minimum amount of luminous material, it having been found that luminous material in excess of from twelveto ilfteen-thousandths of an inch in thickness does not increase the luminosity of the element in proportion to the additional amount of luminous material required, so that a tube of circular cross section providing a luminous line of the desired width may contain a relatively uneconomical excess of the luminous material. Accordingly, at capillary tubes of from twelveto fteen-thousandths of an inch inside thickness and as wide as is required and lled with luminous material, may be provided in accordance with this invention to distinct advantage.

In forming the self-luminous element according to the novel process of this invention, a capillary tube of circular or :dat cross section is "drawn, preferably to considerable length, with a bell at one end to serve as va filling funnel, `the other end of the tube being sealed oli by fusion and the tube filled with dry, nely-divided, radioactive material. The tube so lled is rapidly vibrated mechanically longitudinally, so that the luminous material therein is compacted by impact into a hard, solid, homogeneous column, having a density exceeding that obtainable by any vibration to which it may be subsequently subjected in use, and accordingly it will not thereafter compact and shift 'or slip to vary its original luminous characteristics. It has been found that it is impossible to suiiiciently compact the material in the tube by tapping it by hand, but rather a mechanical impact device, vibrating rapidly, such as at a speed of approximately 3600 vibrations per minute, is essential to secure the proper degree of hardness of the ne, impalpable powder comprising the luminous material.

The tube so illled is then severed into the proper lengths, a small amount of the luminous material removed from one end of each length so that it may be sealed by fusion, and a small amount of the material removed from the other end for the same purpose, except that before sealing of the remaining open end, the tube is exhausted to remove air and any other gases which remain in the tube between the particles of luminous material, and is then sealed by fupractical substitute therefor as compared to the attempts made heretofore to provideself-lumi- -the tubes.

For a better understanding of the invention reference may be had to the accompanying drawing, in which A Figure 1 is an enlarged perspective view of the round form o f the self-luminous element of this invention;

Figure 2 is a similar view of the iiat form ofthe self-luminous element of this invention;

Figure 3 illustrates the compacting machine for compacting the self-luminous material in the elements by impact; v

Figure 4 illustrates the method of expelling the air from the elements before sealing them hermetically;

Figure 5 is an enlarged section of the sealed end of the round element;

Figure 6 is an enlarged section of the sealed end of the at element;

Figure '7 shows a fragment of a grid or grill having its lines formed of the self-luminous elements of this invention; and

VFigure 8 isV an enlarged cross section of a portionof the grid or grill as seen along the linel 8-8 of Figure '1.

In the drawing, numeralfgi designates a capillary glass tube ofgifgcircular cross section, which is drawn in long lengths, such as three to four-feet. In, drawing the capillary tube Ill, one end thereof is preferably provided with a bell II which serves as a filling funnel. The other end Y I2 of the tube Iii is sealed by fusion in a ame, or the like.

Finely-divided, dry, radio-active material A then lintroduced into the bell II while the tube is held in vertical position, so that it is filled from end to end.A The tube is then rapidly vibrated axially or longitudinally by impact. It has been found that tapping the tube by hand is not sufcient to compact the material therein, for, when the nished element is placed on an instrument to illuminate its pointers, dial inscriptions, and the like, and this instrument is mounted on an airplane, vessel or other support subject to a vibration whose-rate is in excess of that originally employed to compact the material in the tube, the material soon becomes compacted to a greater degree, so that it loosens and shifts and accordingly diminishes the effective luminosity of the I required compactness of the luminous material in the tube is illustrated in Figure 3, and consists of a suitable high-speed electric vibrator I3, supported by bars M on a mm frame I5 of suitable construction. Rubber gaskets I6 are preferably interposed between bars I4 and the bolts or other fastening means Il which secure the bars I4 to the frame I5. The vibrator I3 is provided with a platform I8, from which extend upwardlya series of rigid bolts or uprights I9 carrying at their upper ends a cross member 20 secured at opposite sides to the frame I5. The cross member 20 preferably comprises a plate having a plurality of perforations 2l which align with similar perforations 22 in an intermediate plate 23, also supported by the bolts or uprights I9. The bars I4 are extended upwardly above the frame I5 and are provided with a ring 24 for assisting in supporting the elongated tubes Il) when they rest on the platform I8 in the upright position illustrated in Figure 3, after insertion through aligned holes 2| and 22 in cross member 20 and plate 23,

` therein, as much more of the loose luminous material being introduced into the bell II as is necessary to completely iill the tube to the desired height. The tube I0 containing the selfluminous material 25 accordingly becomes in effect a unitary element, the self-luminous material being so firmly compacted therein.

The filled tube I0 is then severed or broken into appropriate lengths, depending upon requirements, and a small amount'of the self-luminous material is removed from each end of each length so that these ends may be sealed by fusion. One end of the tube is then sealed at 26 in this way. In order to expel the air in these filled lengths of tube, they are passed relatively slowly through a flame 2l in a direction leading from the sealed end 26 toward the unsealed end, as is illustrated in Figure 4, so that the air contained in the tube is substantially entirely expelled therefrom by the heat, which should not be sufficient to injure the material 25. When' the tube I0 has been passed entirely through the flame 21, but before its open end is withdrawn out of the flame, this open end is sealed by fusion in the flame, so that no air can enter the tube after it has been exhausted in the manner described. The partial vacuum thus formed in the tube causes the molten glass at the end being sealed to be drawn into the end of the tube to form a smooth rounded end 28, illustrated in Figure 5, engaging the corresponding end of the column of radio-active material 25 in the tube IIJ. In this way, the objectionable enlarged ball, which is formed in sealing the remaining open end o f an unexhausted tube, is avoided. This isan important consideration, because such tubes are frequently mounted in slots or grooves which will not admit any oversized portions of the tube. Other methods of exhausting the tube I0 prior to sealing its remaining 'open end lie within the scope of this invention.

In a modied form of the invention, iiat, ribbonlike, glass capillary tubes are drawn with an inside thickness not substantially exceeding fteenthousandths of an inch and a considerably greater inside width, depending upon requirements. I have found that self-luminous material in excess of from twelveto fifteen-thousandths of an inch in thickness does not increase the lumiquired, so that a tube of circular cross section providing a luminous line of the desired Width contain a relatively uneconomical excess' of the luminous material. Also, the flat tube is easier to handle and more adaptable to application on various thin objects without materially increasing the over-al1 thickness of the assembly, which is .not the case' withcircular cross section tubes providing an equivalent degree of luminosity.

, lo" to avoidv the formation of a ball across the narrow These flat ltubes I' are filled in' the 'same way as the circular round tubes I0, but in sealing the ends of the tube a different procedure is,v necessary portion of the tube end. This procedure involves ilrst reducing the end of the tube to a point as aty II in Figure 6, and then it is sealed by fusion at 3l, the -tube being exhausted before the re..

-vmaining openl end is sealed. The fused end Ii yaccordingly is nothicker' than the minimum thickness of the nished at tube I Il'.

' The dat tube Illis admirably adapted for forming luminous grids and grills, because when it is applied to the surface t0 be illuminated, it

provides a maximum width of luminous line for a minimum increase in thickness of the assembly.v

Furthermore, instead of mounting the flat tube Lil' on the surface of the glass plate 3| forming the base of the grid or grill, parallel grooves may ,b e ground or otherwise formed in one surface of the plate ll and the ilat elements Il set flush with its surface. Crossing lines may be formed by grinding or otherwiseV forming grooves twiceas deep in a crossing direction in the surface of the plate'll and setting crossing elements'l' in'slots ground or otherwise formed in the reverse i face of theplate I0. i y Instead of forming self-luminous grids or grills in ther manner described, the tubes I0 or I0' may be placed in closely-spaced, parallel positions `ontransparent, translucent, or opaque surfaces to render such surface luminous in the dark for the purpose of providing markers of circular or other shapes for various uses. Also, the elements l ofl this inventionhave many ther uses.

It will be seen that the new self-luminous element made in accordance-with the novel method of this invention is devoid gif the objectionable features of luminous paint heretofore employed and of-capiliary tubes heretofore proposed containing loose self-luminous material.

While )referred embodiments of the invention have been illustrated and described. it

,istobe understood that the invention is not lim-v fished element is subsequently subjected in use.

'pacting the `material by vibrating the tube end- AWiseat a rate exceeding that to which the n- Vished element is subsequently subjected in use,

ited thereby. but is susceptible of various chang in form and detail within its scope.

1. The'method vof Amaking self-luminous ele.` ments, which comprises filling an elongated glass 5 t'ube with self-luminous material. said tube being y closed at one end, expelling surplus air from the tube by passing the tube through a flame from the closed end to the open end, and sealing the open end by fusion in the flame without withdrawing the tube from the flame after the airexpelling operation.

2. 'I'he method of making self-luminous ele ments which comprises lling an elongated glass tube with dry powdered self-luminous material, said tube being closed at one end. tightly compacting the material by vibrating the tube endwise at a rate exceeding that to which the nnexpelling surplus air from the tube by passing the tube through a ame from the closed end to' the open end, and sealing the open end by fusion in a the llame without withdrawing the tube from the ilameE after the airexpelling operation. I

whereby themolten glass at the sealedV tube end; 2g

is drawn inwardly and an enlargement at the: sealed tube end is avoided. y 3. Ihe method of making self-luminous ele-1 ments which comprises filling an elongated glass tube' with dry powdered self-luminous material,

said tube being closed at one end, tightly comendwlse impacts at a frequency exceeding that of any vibration to which the finished element is subsequently subjected in use, expelling surplus 35 'air `from the tube by passing the tube through a flame from the closed` end to the open end thereof and sealing the open end of the tube by fusion in the arne without withdrawlngthe tube from the flame after the air-expelling operation.

4. 'I'he method of making self-luminous ele-` ments which comprises lling an elongated'glass tube with dry powdered self-luminous material. said tube being closed at one end, tightly comsevering at least one short nlled section from said tube, removing a' small amount of the compacted self-luminous material from each end of said 50 llame from the closed-end'to the open end and sealing the open end by fusion in the flame without withdrawing the tube from the flame after the air-expelling operation.

JOHN E. PAUL.

'pacting the material by subjecting the tube t0. l, 

